The present invention relates generally to hermetic compressors, and more particularly to compressors of the scroll type.
Refrigeration and air conditioning systems generally include a compressor, a condenser, an expansion valve (or equivalent), and an evaporator, coupled in sequence in a continuous flow path. A working fluid or refrigerant flows through the system and alternates between a liquid phase and a vapor or gaseous phase.
A variety of compressor types may be used in refrigeration systems, such as reciprocating, screw, or rotary, including vane and scroll machines. Scroll compressors are constructed with two scroll members, each having an end plate and a spiral wrap, arranged in an opposing manner with the spiral wraps interfitted. The scroll members are mounted so that the scroll members may engage in cyclical orbiting motion with respect to each other. During this cyclical orbiting movement, the spiral wraps define a successive series of enclosed spaces, each of which progressively decreases in size as it moves inwardly from a radially outer position at a relatively low suction pressure to a central position at a relatively high central pressure. The compressed gas exits from the enclosed space at the central position through a discharge passage formed through the end plate of one of the scroll members.
Under any one of a number of adverse conditions, the discharge gas can become excessively hot, which can adversely effect efficiency and the durability of the compressor. One known method of cooling the compressed gas is to inject liquid refrigerant from the outlet of the condenser through an injection passage directly into the compressor. The liquid may be injected into the suction gas area of the compressor, or into an intermediate enclosed space defined by the scroll members. These methods are variously shown in U.S. Pat. No. 5,076,067, entitled "Compressor With Liquid Injection", and U.S. Pat. No. 4,974,427, entitled "Compressor System With Demand Cooling", and patent application Ser. No. 07/912,908, filed on Jul. 13, 1992, U.S. Pat. No. 5,329,788, entitled "Scroll Compressor With Liquid Injection", all of which are assigned to the same assignee as the present application, the disclosures of which are hereby incorporated herein by reference. It is desirable for maximum effective cooling of the discharge gas that the liquid injection port be located as centrally, or as close to the discharge passage, as is possible. Unfortunately, however, the location of the injection port is limited by the liquid supply pressure at the outlet of the condenser, which is intermediate the suction pressure and discharge pressure of the compressor. If the pressure of the gas in an enclosed space near the discharge port is greater than the condenser outlet liquid supply pressure throughout an entire cycle of orbiting motion, then no liquid refrigerant can flow to the enclosed space in the compressor from the liquid injection passage.
It is therefore desirable to lower the pressure of the central enclosed space to below the liquid supply pressure during at least a portion of the cycle of orbiting movement, to enable positive injection through a more centrally located injection port (i.e. closer to the discharge port where the gas is hottest, and where cooling is most effective). One method of lowering the pressure in the central enclosed chamber is the use of a dynamic one-way valve in the discharge passage which opens and closes once every cycle. Such valves, however, are often noisy, unreliable, and reduce compressor efficiency due to valve losses in normal operation. They also add additional cost for the extra hardware, as well as for assembly.
In contrast, the present invention provides a unique configuration which includes a liquid injection passage in combination with a discharge diffuser for reducing the pressure in the enclosed spaces, allowing liquid injection at a later time in the cycle, from a more central position, thereby enabling more effective cooling of the working fluid.
Moreover, liquid injection systems having one injection port are generally capable of injecting liquid into only one of the enclosed spaces defined by the scroll members during each cycle of orbiting motion. It is desirable to provide a liquid injection system having only one injection port, yet which is capable of injecting liquid into more than one of the enclosed spaces in each cycle of orbiting motion.
The present invention has as its object the obviation of the problems associated with the current art by providing a uniquely configured liquid injection apparatus which provides highly effective cooling.
The various advantages and features will become apparent from the following description and claims in conjunction with the accompanying drawings: